1. Field of the Invention
The present invention is directed to providing a compact sensor for measuring wavefront phase, particularly a compact sensor which is compatible with micro-electro-mechanical systems.
2. Description of Related Art
The most common wavefront sensors measure wavefront slope. Such sensors include Hartmann and Shearing sensors. A Shearing interferometer displaces an incoming wavefront laterally by a small amount and analyzes the interference pattern between the original and the displaced wavefront. The resulting interference pattern relays information regarding any distortions in the incoming wavefront. There are many physical arrangements for obtaining lateral shear, but none have yet been developed on a small scale. This is due primarily to the requirement of the two beams for interference.
A Hartmann sensor breaks the aperture into an array of subapertures. Each subaperture has a lenslet to focus the light onto a subarray of detectors. Tilts in the subaperture wavefronts are detected by the centroid motion of the focal spot on the subarray of detectors. The Hartmann sensor can be used to create a wavefront camera. However, the Hartmann sensor requires the computation of subarray centroids. This computation is difficult to perform on a chip. The Hartmann sensor subarrays also require pixel non-uniformity gain and offset correction for low noise wavefront slope measurement.
The Hartmann sensor is based on the premise that a wavefront can be sampled in a number of locations across the wavefront in a predetermined fashion. The wavefront can then be reconstructed by relating the sample points to each other. The Hartmann sensor does not require two beams, since it is a screen test, not an interferometer. Thus, the Hartmann sensor is based purely on geometrical optics. As noted above, the Hartmann sensor is computationally inelegant and has limited application.